The present invention is directed, in general, to wireless communications systems and, more specifically, to a system for monitoring adjacent channel power in a base station transmitter in a wireless communication network.
Reliable predictions indicate that there will be over 300 million cellular telephone customers by the year 2000. Within the United States, cellular service is offered by cellular service providers, by the regional Bell companies, and by the national long distance operators. The enhanced competition has driven the price of cellular service down to the point where it is affordable to a large segment of the population.
To maximize usage of the available bandwidth, a number of multiple access technologies have been implemented to allow more than one subscriber to communicate simultaneously with each base transceiver station (BTS) in a wireless system. These multiple access technologies include time division multiple access (TDMA), frequency division multiple access (FDMA), and code division multiple access (CDMA). These technologies assign each system subscriber to a specific traffic channel that transmits and receives subscriber voice/data signals via a selected time slot, a selected frequency, a selected unique code, or a combination thereof.
In order to further increase the number of subscribers that can be serviced in a single wireless network, frequency reuse is maximized by making individual cell sites smaller and using a greater number of cell sites to cover the same geographical area. Accordingly, the greater number of base transceiver stations increases infrastructure costs. To offset this increased cost, wireless service providers are eager to implement any innovations that may reduce equipment costs, maintenance and repair costs, and operating costs, or that may increase service quality and reliability and the number of subscribers that the cellular system can service.
Every wireless network base station has an RF power amplifier for transmitting voice and/or data signals to mobile units (i.e., cell phones, portable computers equipped with cellular modems, pagers, and the like) and a receiver for receiving voice and/or data signals from the mobile units. The FCC requires an RF power amplifier (PA) to be operated in such a manner that the adjacent channel power (ACP) noise (distortion) remains under certain limits (i.e., a mask) defined in a standard (i.e., ACP profile). ACP is the ratio of adjacent channel power in a specified bandwidth to the power of the desired transmitter output.
To ensure that the ACP profiles of network base stations remain within tolerance, wireless service providers frequently measure the RF output power and signal quality of each base station transmitter. However, the test equipment used typically includes a spectrum analyzer that costs far more that the base station transmitter itself. Due to this great cost, the test equipment rarely is implemented as part of the base station itself. Instead, maintenance crews transport the test equipment from cell site to cell site to perform ACP profile tests. Unfortunately, this does not provide real-time monitoring of ACP noise and distortion products in a wireless network. RF transmitters that are out-of-tolerance are not detected until a maintenance crew finally tests the equipment.
There is therefore a need in the art for test equipment that may be implemented as part of the base station. In particular, there is a need for test equipment that provides continuous monitoring of adjacent channel power (ACP) noise in wireless network base stations. More particularly, there is a need for ACP monitoring equipment that is reliable, adds the minimum amount of cost to a base station, and provides a remote monitoring capability for ACP noise.
To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to provide an ACP monitoring circuit for use in a wireless network comprising a plurality of base stations capable of communicating with a plurality of mobile devices, wherein each of the plurality of base stations comprises an RF transmitter capable of receiving an input baseband signal and an RF carrier signal and producing therefrom an amplified modulated RF output signal. In an advantageous embodiment of the present invention, the ACP monitoring circuit, capable of monitoring adjacent channel power (ACP) noise in the RF output signal, comprises: 1) an RF mixer having a first input capable of receiving the RF output signal and a second input capable of receiving the RF carrier signal and producing therefrom a scaled output signal on an output of the RF mixer; and 2) a first power detection circuit coupled to the RF mixer and capable of determining a power level of the ACP noise outside an allocated channel bandwidth of the RF transmitter.
In one embodiment of the present invention, the ACP monitoring circuit further comprises a filter coupled to the RF mixer for isolating the ACP noise, wherein the first power detection circuit measures the power level of the ACP noise at an output of the filter.
In another embodiment of the present invention, the ACP monitoring circuit further comprises a second power detection circuit coupled to the RF mixer and capable of determining a power level of the RF output signal in the allocated channel bandwidth of the RF transmitter.
In still another embodiment of the present invention, the ACP monitoring circuit further comprises a filter coupled to the RF mixer for isolating the RF output signal, wherein the second power detection circuit measures the power level of the RF output signal at an output of the filter.
In yet another embodiment of the present invention, the ACP monitoring circuit further comprises: 1) a first filter coupled to the RF mixer for isolating the ACP noise; and 2) a second filter coupled to the RF mixer for isolating the RF output signal, wherein the first power detection circuit measures the power level of the ACP noise at an output of the first filter and measures a power level of the RF output signal in the allocated channel bandwidth of the RF transmitter at an output of the second filter.
In a further embodiment of the present invention, the ACP monitoring circuit further comprises a switch having a first input coupled to the first filter output, a second input coupled to the second filter output, and an output coupled to the first power detection circuit.
In a still further embodiment of the present invention, the ACP monitoring circuit further comprises at least one bandpass filter coupled to the RF mixer for isolating the ACP noise, wherein the first power detection circuit measures the power level of the ACP noise in a first selected frequency band at an output of the bandpass filter.
In a yet further embodiment of the present invention, the ACP monitoring circuit further comprises a plurality of bandpass filters coupled to the RF mixer for isolating the ACP noise, wherein the first power detection circuit measures the power level of the ACP noise in a plurality of selected frequency bands at an output of the bandpass filter.
The foregoing has outlined rather broadly the features and technical advantages of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features and advantages of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they may readily use the conception and the specific embodiment disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.
Before undertaking the DETAILED DESCRIPTION, it may be advantageous to set forth definitions of certain words and phrases used throughout this patent document: the terms xe2x80x9cincludexe2x80x9d and xe2x80x9ccomprise,xe2x80x9d as well as derivatives thereof, mean inclusion without limitation; the term xe2x80x9cor,xe2x80x9d is inclusive, meaning and/or; the phrases xe2x80x9cassociated withxe2x80x9d and xe2x80x9cassociated therewith,xe2x80x9d as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like; and the term xe2x80x9ccontrollerxe2x80x9d means any device, system or part thereof that controls at least one operation, such a device may be implemented in hardware, firmware or software, or some combination of at least two of the same. It should be noted that the functionality associated with any particular controller may be centralized or distributed, whether locally or remotely. Definitions for certain words and phrases are provided throughout this patent document, those of ordinary skill in the art should understand that in many, if not most instances, such definitions apply to prior, as well as future uses of such defined words and phrases.